The present invention relates to a device transfer method of transferring devices such as semiconductor light emitting devices, and to a device array method and an image display unit production method, which are adapted to transfer finely formed devices to a wider region by making use of the device transfer method.
Two methods have generally been employed to produce image display units having light emitting devices arrayed in a matrix. One method, which is used for producing liquid crystal displays (LCDs) or plasma display panels (PDPs), is carried out by directly forming devices on a substrate. The other method, which is used for producing light emitting diode (LED) displays, is carried out by packaging each LED, and arraying the single LED packages on a substrate. In the case LCD or PDP display units, device isolation is impossible due to the structure of the device. Therefore, such devices are generally formed, from the beginning of the production process, in such a manner as to be spaced from each other with a pitch equivalent to a pixel pitch of a final image display unit.
On the other hand, in the case of producing LED displays, LED chips obtained by dicing are individually connected to external electrodes by wire-bonding or bump-connection using flip-chip packaging techniques. In this case, before and after packaging, the LED chips are arrayed with a pitch equivalent to a pixel pitch of the final image display unit; however, such a pixel pitch is independent of the pitch of the devices at the time the devices are formed.
Since LEDs (Light Emitting Diodes) as individual light emitting devices are expensive, an image display unit using LEDs can be produced at a lower cost by producing a number of LEDs from one wafer. To be more specific, the cost of an image display unit can be reduced by preparing LED chips while reducing a size of each LED chip from a conventional size of about 300 xcexcm square into a size of several ten xcexcm square, and connecting the LEDs chips to each other, to produce the image display unit.
From this viewpoint, there have been known various techniques of transferring devices densely formed on a substrate to a wide region in a manner such that the devices are spaced further apart from each other in the wide region, thereby obtaining a relatively large display unit such as an image display unit. For example, U.S. Pat. No. 5,438,241 has disclosed a thin film transfer method, and Japanese Patent Laid-open No. Hei 11-142878 has disclosed a method of forming a transistor array panel for display. In the transfer method disclosed in U.S. Pat. No. 5,438,241, devices densely formed on a substrate are coarsely re-arrayed by transferring the devices densely formed on the substrate to an extensible substrate provided with an adhesive layer, extending the extensible substrate in the X direction and the Y direction while monitoring a device array pitch and positions of respective devices, and transferring the devices on the extended substrate onto a desired display panel. In the technique disclosed in Japanese Patent Laid-open No. Hei 11-142878, thin film transistors forming a liquid crystal display portion on a first substrate are all transferred onto a second substrate, and the thin film transistors are selectively transferred from the second substrate to a third substrate in such a manner that the transferred transistors are spaced apart from one another on the third substrate with a pitch corresponding to the pixel pitch of the display unit.
In the case of producing image display units by the above-described transfer techniques, it is required to selectively, certainly transfer only devices to be transferred, and to efficiently, accurately transfer only devices to be transferred.
An object of the present invention is to provide a device transfer method capable of certainly, efficiently, and accurately transferring, among devices formed on a substrate, only those to be transferred, and a device array method and an image display unit production method using the device transfer method.
To achieve the above object, according to a first aspect of the present invention, there is provided a device transfer method of transferring a number of devices arrayed on a first substrate to a second substrate. The method includes covering the devices on the first substrate with a release agent. A portion of the release agent positioned on a device to be transferred is then selectively removed. The first substrate is then placed on a second substrate in such a manner that the devices arrayed on the first substrate face an adhesive layer previously provided on the second substrate. The device from which the release agent has been removed is then irradiated from a back side of the first substrate, and the second substrate is peeled from the first substrate.
Devices covered with a release agent have small adhesive forces against an adhesive layer by the effect of the release agent, while a device from which the release agent has been removed is adhesively bonded to the adhesive layer with a specific adhesive force. At the same time, since only the device from which the release agent has been removed is irradiated with a laser beam from a back side of a substrate, the device is peeled from the substrate by so-called laser abrasion. As a result, according to the device transfer method of the present invention, only the device from which the release agent has been removed can be readily, selectively transferred to a second substrate side by the adhesive force and the peeling from the substrate by laser abrasion.
According to a second aspect of the present invention, a device array method of re-arraying a plurality of devices, which have been arrayed on a first substrate onto a second substrate is provided. The method includes a first transfer step of transferring the devices from the first substrate to a temporary holding member in such a manner that the devices are enlargedly spaced from each other on the temporary holding member with a pitch larger than a pitch of the devices arrayed on the first substrate. The devices are then held on the temporary holding member. A second transfer step involves transferring the devices held on the temporary holding member to a second substrate in such a manner that the devices are more enlargedly spaced from each other on the second substrate with a pitch larger than a pitch of the devices held on the temporary holding member. The first transfer step further includes the steps of covering the multiple devices on the first substrate with a release agent and selectively removing a portion of the release agent, positioned on a device to be transferred. The transfer step further includes placing the first substrate on the temporary holding member in such a manner that the devices arrayed on the first substrate face an adhesive layer previously provided on the temporary holding member. The transfer step next involves irradiating the device from which the release agent has been removed, from a back side of the first substrate, then peeling the temporary holding member from the first substrate.
With this configuration, since the transfer of devices is efficiently, certainly performed, it is possible to smoothly perform transfers in which the device pitch is enlarged. To be more specific, devices on a first substrate are smoothly transferred to a second substrate via a temporary holding member in such a manner that the devices are enlargedly spaced from each other on the second substrate, having a pitch larger than a pitch of the devices on the first substrate.
According to a third aspect of the present invention, there is provided an image display unit production method of producing an image display unit in which light emitting devices are arrayed in a matrix. The production method involves a first transfer step of transferring light emitting devices from a first substrate to a temporary holding member in such a manner that the light emitting devices are enlargedly spaced from each other on the temporary holding member with a pitch larger than the pitch of the light emitting devices when they are arrayed on the first substrate. The light emitting devices are then held on the temporary holding member. A second transfer step involves transferring the light emitting devices held on the temporary holding member to a second substrate in such a manner that the light emitting devices are more enlargedly spaced from each other on the second substrate, having a pitch that is larger than the pitch of the light emitting devices when they are held on the temporary holding member. A wiring formation step is provided for forming wiring connected to the light emitting devices. To accomplish this the first transfer step further includes the step of covering the plurality of light emitting devices on the first substrate with a release agent. A portion of the release agent positioned on a light emitting device to be transferred is then selectively removed. The first substrate is stuck to the temporary holding member in such a manner that the light emitting devices arrayed on the first substrate face an adhesive layer previously provided on the temporary holding member. The light emitting device from which the release agent has been removed is irradiated from a back side of the first substrate and the temporary holding member is peeled from the first substrate.
Using the above described device transfer method and device array method, it is possible to efficiently, enlargedly re-array light emitting devices, which have been densely formed, that is, finely formed with a high degree of integration, thus, it is possible to significantly improve the productivity of the image display unit.